A typical brake system uses one or more friction assemblies. A friction assembly is a replaceable element. A friction assembly comprises a brake pad having a friction material mounted on a backing plate. For example, in a typical disc brake, a rotating disc or rotor rotates with a wheel of a vehicle. A pair of opposing friction assemblies are positioned on opposite sides of the rotor such that both friction materials face to the rotor. Outside the friction assemblies are a piston and a corresponding caliper, respectively. When the brake is actuated and the piston and caliper are advanced closer to each other, the friction assemblies are pressed against the rotor between the piston and caliper. Thus, the friction materials contact the rotor to provide a stopping frictional force.
Significant forces are involved in applying the friction materials to the rotor. Due to the relative movement during the engagement of the friction materials and the rotor, squeal noise can be produced. In order to reduce the squeal noise, it is known to attach a noise damping shim to the brake pad.
The noise damping shim is typically attached to the backing plate of the brake pad using pins or staples through holes formed on the backing plate and shim. In this construction, the shim is subject to significant torques between the friction assembly and the piston or caliper pushing the shim against the brake pad during the braking operation. In order to minimize movements of the shim relative to the brake pad, the pins and holes need to be precisely dimensioned. Also, the use of pins increases the number of components to be assembled, which increases manufacturing costs.
In some friction assemblies, a noise damping shim has tabs or hooks projecting outwardly from the periphery of the shim. When the shim is attached to a backing plate, the hooks are bent and engaged to the backing plate. This type of friction assembly is advantageous for requiring fewer components to be assembled compared to the friction assemblies that use pins. However, the provision of the tabs require additional shim materials and the hook bending process during the assembling requires a complicated assembling machine.
It is therefore desirable to provide a backing plate having improved engagement between a brake pad and a noise damping shim without involving undue extra manufacturing costs.